Tissue irradiator

ABSTRACT

A tissue irradiator is provided for the in-vivo irradiation of body tissue. The irradiator comprises a radiation source material contained and completely encapsulated within vitreous carbon. An embodiment for use as an in-vivo blood irradiator comprises a cylindrical body having an axial bore therethrough. A radioisotope is contained within a first portion of vitreous carbon cylindrically surrounding the axial bore, and a containment portion of vitreous carbon surrounds the radioisotope containing portion, the two portions of vitreous carbon being integrally formed as a single unit. Connecting means are provided at each end of the cylindrical body to permit connections to blood-carrying vessels and to provide for passage of blood through the bore. In a preferred embodiment, the radioisotope is thulium-170 which is present in the irradiator in the form of thulium oxide. A method of producing the preferred blood irradiator is also provided, whereby nonradioactive thulium-169 is dispersed within a polyfurfuryl alcohol resin which is carbonized and fired to form the integral vitreous carbon body and the device is activated by neutron bombardment of the thulium-169 to produce the beta-emitting thulium-170.

United States Patent [1 1 Hungate et a1.

11] 3,927,325 1451 Dec. 16, 1975 TISSUE IRRADIATOR [75] Inventors: FrankPorter Hungate, Kennewick;

William Frederic Riemath, Pasco; Lee Roy Bunnell, Kennewick, all ofWash.

[73] Assignee: The United States of America as represented by the UnitedStates Energy Research and Development Administration, Washington, DC.

[22] Filed: July 10, 1974 [21] Appl. No.: 487,327

[52] US. Cl. 250/435; l28/l.l; 250/493 [51] Int. (31. A61N 5/12;G01N21/24; 621G 4/00 [58] Field of Search 117/46 CB; 250/432, 435, 250/436,437, 438, 492, 493; 128/141, 1.2

[56] References Cited UNITED STATES PATENTS 3,434,467 3/1969 Anderson eta1. 250/435 X 3,705,985 12/1972 Manning et al 250/435 3,811,426 5/1974Culver et a1. l28/l.2 3,854,979 12/1974 Rossi 117/46 CB Primary Examinerlaul L. Gensler Assistant ExaminerT. N. Grigsby Attorney, Agent, orFirm-Dean E. Carlson; Arthur A. Churm; Robert J Fisher 5 7 ABSTRACT Atissue irradiator is provided for the in-vivo irradiation of bodytissue. The irradiator comprises a radiation source material containedand completely encapsulated within vitreous carbon. An embodiment foruse as an in-vivo blood irradiator comprises a cylindrical body havingan axial bore therethrough. A radioisotope is contained within a firstportion of vitreous carbon cylindrically surrounding the axial bore, anda containment portion of vitreous carbon surrounds the radioisotopecontaining portion, the two portions of vitreous carbon being integrallyformed as a single unit. Connecting means are provided at each end ofthe cylindrical body to permit connections to bloodcarrying vessels andto provide for passage of blood through the bore. 1n a preferredembodiment, the radioisotope is thulium-170 which is present in theirradiator in the form of thulium oxide. A method of producing thepreferred blood irradiator is also provided, whereby nonradioactivethulium-169 is dispersed within a polyfurfuryl alcohol resin which iscarbonized and fired to form the integral vitreous carbon body and thedevice is activated by neutron bombardment of the thulium-169 to producethe beta-emitting thulium-170.

10 Claims, 2 Drawing Figures US. Patent Dec. 16, 1975 TISSUE IRRADIATORCONTRACTUAL ORIGIN OF THE INVENTION The invention described herein wasmade in the course of, or under, a contract with the UNITED STATESATOMIC ENERGY COMMISSION.

BACKGROUND OF THE INVENTION This invention relates to radiotherapy andto in-vivo radiation treatment of body tissues with particular emphasisdirected toward in-vivo radiation treatment of blood. Specifically, thepresent invention is directed toward a flow-through blood irradiationdevice for implantation within the body, which device is both smallerand lighter than previously available flowthrough radiation devices.Additionally, the development of this device has been accompanied by thedevelopment of techniques for production of the device with increasedsafety in dealing with the radioisotope used in the radiation device.

Radiotherapy, incuding radiation treatment of blood, as a potential cureor control for various diseases is wellknown in the art, radiotherapybeing extensively used in treating various forms of cancer. Two areas towhich radiotherapy has been found to be particularly adaptable are thecontrol of leukemia and the control of immune reactions initiated bylymphocytes following tissue transplants. Suppression of lymphocytelevels in circulating blood following irradiation of the total body withlow doses of ionizing radiation is well-known. It has been demonstratedthat irradiation of blood in an exterior blood loop (extracorporealirradiation of blood) suppresses lymphocyte levels without damage toother body tissues. It has consequently been shown that extracorporealirradiation of blood is an effective adjunct or alternative to drugtherapy for treating some forms of leukemia.

Immune reactions initiated by lymphocytes are usually the ultimatereason for failure of organ transplants. Current methods of suppressingthese immune reactions include use of drug therapy, antilymphocyteantibodies and irradiation. Typically, more than one of these approachesis used, since there are problems associated with each. Acceptance timesof skin allografts have been extended by extracorporeal irradiation ofblood and this technique has been evaluated for its applicability forimmunosuppression relative to renal allografts. Significant reduction inearly rejection episodes and a significantly higher frequency of 6-month renal graft survival has been reported for extracorporealirradiation of blood treated groups.

While this type of blood irradiation to suppress tissue and organrejection and to control some blood diseases has been shown to besuccessful at locations fortunate enough to have irradiators, there issome evidence that continuous irradiation of blood may be more effectivethan periodic acute irradiations. Most treatments of both experimentalanimals and humans have been accomplished by shunting blood throughlarge fixed equipment containing cobalt-60, cesium-13 7 or X-raysources, thereby necessitating specialized facilities. With relativelylong treatment regimes required, this severely limits the number ofpatients who can receive treatments and requires the inconvenience andexpense of hospitalization. Effortshave been directed toward thedevelopment of small, inexpensive, portable irradiators to permitchronic exposures of patients. In particular, it is desirable to designa small, implantable irradiation device which would permit directin-vivo irradiation of the blood. A radioisotope-coated wire forinsertion diagonally across a blood vessel was previously described inUS. Pat. No. 3,811,426, coinvented by one of the present applicants.

Another type of irradiator which has been under development is a small,tubular irradiator which provides for blood flow through the tube, theirradiator device being surgically inserted so as to serve as a smallsection of the blood vessel. Irradiators of this type made to date haveused very energetic beta emitters, such as strontium--yttrium-9O orphosphorus-32. One such device contained 2 curies of strontium-90-'yttrium-9O in a cylindrical zone 1 cm long within an approximately 25mm thick outer layer of Hevimet shielding. A 0.025 mm thick layer oftitanium covered the strontium-yttrium source. A thin-walled Silastictubing, 2.64 mm inner diameter and 3.66 mm outer diameter, served totransport the circulating blood through the irradiator. The blood doserate, estimated by passing Fricke dosimeter solution through theSilastic tubing at known flowrates and measuring the optical densitychange, provided a transit dose to the blood estimated to be 40 rads ata flow rate of ml/min. The total weight of this irradiator was justunder 2 kg. Because a device of this nature using the energetic betaemitters will induce hard bremsstrahlung, it is essential thatsubstantial shielding be provided to protect surrounding tissues. Theneed for this substantial shielding results in devices which are heavyand cumbersome and such devices presently in use generally weigh severalpounds. Silastic tubing is also disadvantageous in that embrittlementupon irradiation is a frequent problem.

It is an object of the present invention to provide a device forirradiation of body tissues.

It is a further object of the present invention to provide a device forin-vivo irradiation of blood.

Another object of the present invention is to provide an implantabledevice for continuous in-body irradiation treatment of blood flowingthrough the circulatory system.

Another object of the present invention is to provide a radiation devicefor the treatment of blood which will not give off undue irradiation tosurrounding body tissues.

A further object of the present invention is to provide an in-vivo bloodirradiation device for which substantial shielding is not required andwhich therefore permits construction of a lightweight device.

Other objects and advantages of the present invention will becomeapparent upon reading the following description and with particularreference to the specific embodiment described hereinbelow.

SUMMARY OF INVENTION In accordance with the present lfivention, chronicin-vivo radiation treatment of tissue earl be conducted by implantationof an improved lightweight portable irradiator. The tissue irradiator ofthe present invention has a radioisotope material contained Ill 3H6encapsulated by vitreous carbon. The radioisote E is suspended in afirst portion of vitreous carbon whle is surrounded and encapsulated bya containment pofilii of the vitreous carbon. The vitreous carbon is inegrally formed as a single mass with the two portions Beinginsegmentable and indiscernible except for the presence of theradioisotope in a portion of the unit body. The formation of thevitreous carbon as a single unit provides improved containment of theradioactive material. 4

Particular embodiments of the invention are directed toward in-vivoirradiation of blood. In these blood irradiator embodiments, thevitreous carbon is in the form of a cylindrical body with an axial boreto permit flow of blood through the body. The radioisotope material iscontained in a tubular portion of the vitreous carbon which surroundsthe bore and lies fully within the vitreous carbon containment body.Means are provided for connecting this cylindrical body to blood vesselsin order to pass blood through the bore. In preferred embodiments, theradioisotope is thulium-170 which preferably is present as Tm O Use ofthulium permits construction of the device employing thulium-169 whichcan be activated to the radioactive beta emitter thuliuml 70 by neutronactivation after basic construction of the device has been completed.

BRIEF DESCRIPTION OF THE DRAWINGS An understanding of the features andthe advantages offered by the present invention can be obtained from areading of the following description and with reference to the drawings,in which:

FIG. 1 is a sectional view of a device in accordance with the presentinvention; and

FIG. 2 is a cross-sectional view of the device taken along the line 2-2of FIG. 1.

DESCRIPTION OF THE INVENTION In its broadest aspects, the presentinvention is directed toward tissue irradiators which can be implantedfor in-vivo radiation treatment of various body tissues. In accordancewith the broadest aspects of the present invention, a radiation sourcematerial, such as a radioisotope, is dispersed and suspended within avitreous carbon body. Vitreous carbon or glassy carbon is a term knownin the art and refers to a glasslike form of carbon having no definedcrystal structure. The vitreous carbon surrounds and encapsulates eashof the radiation source material particles and, in addition, forms acontainment layer completely surrounding the radiation source material.The vitreous carbon is integrally formed as a single unit body. Whilethe radiation source material lies in a well defined differentiableregion or zone of the body, the vitreous carbon itself exists as a unitmass with the two portions, a first portion containing the sourcematerial and a containment portion surrounding the first portion, beinginsegmentable and indiscernible as separate layers except for thepresence of the source material. Other features of the particularirradiator will depend upon the type of radiation desired, the strengthof radiation desired and the particular tissue which is to beirradiated. The use of vitreous carbon offers several advantages.Vitreous carbon is a biocompatible material. Also, since carbon is verylittle afi'ected by irradiation, even at intensities near the core ofnuclear reactors, there will be little change in the properties of theirradiator after long periods of time. Problems could develop withprevious types of irradiators in that components of the irradiator bodycould become embrittled upon prolonged exposure to radiation.Additionally, since the vitreous carbon is a low Z material (low atomicweight), there will be a minimum amount of bremsstrahlung radiationproduced from this device. This permits construction of a device withoutthe need for extra shielding material to prevent bremsstrahlungradiation damage to surrounding tissues.

The present invention has been found to be particularly adaptable toembodiment as an in-vivo blood irradiator. While the invention will bedescribed with reference to this specific embodiment, the invention isnot limited to this particular embodiment but should be construed withthe broader aspects of the invention as herein discussed. For example,the irradiator could be shaped as a flat plate for tissue or organirradiation, or as a solid needle for intra-tissue irradiation.

Referring now to the drawings for assistance in the description of thespecific embodiment of the present invention, there is shown in FIG. 1and FIG. 2 a blood irradiator indicated generally at 11. A radiationsource material 12 is contained in and encapsulated by a unit mass ofvitreous carbon 13. The vitreous carbon mass 13 consists of a tubularfirst portion 14 which contains the radiation source material 12 andencapsulates on a microscale each of the particles of the radiationmaterial 12 and a containment portion 15 insegmentable from firstportion 14 and indiscernible therefrom except for the presence of thesuspended radiation source material 12. The containment portion 15encapsulates the radiation source material 12 on a macroscale. Thecontainment portion 15 forms a cylindrical body having an axial bore 16.The first portionof vitreous carbon 14 in which the radiation sourcematerial is dispersed and suspended lies cylindrically about bore 16 andis fully surrounded and encapsulated by the containment portion 15. Athin layer 17 0f the containment portion 15 lies interiorly to thetubular first portion of vitreous carbon 14. The tubular first portionof vitreous carbon 14 is surrounded exteriorly by a thick layer 18 ofthe containment portion of vitreous carbon 15. The layer 17 is thin soas to permit penetration of the radiation from source material l 2'intothe bore 16 while layer 18 is thicker to provide significant shielding.While the vitreous carbon has been described as consisting of variousportions, it should be understood that in actuality the vitreous carbonis integrally formed as a single unit and, while one can; refer tovarious portions or layers for sake of description, the vitreous carbonitself is not segmented but is a single mass. In a preferred embodimentof the present invention, a pyrolytic graphite tube 19 extends throughthe device 11 within bore 16. The pyrolytic graphite lt'ube serves as ablood conduit through the device and is preferred because of thenonthrombogenic nature of pyrolytic graphite. The containment of theradiation source material within vitreous carbon offers an advantage inthat the radioactive particles are encapsulated on both a microand amacroscale. The individual particles are encapsulated in what isreferred to as the first portion of vitreous carbon 14. On a macroscalethis entire portion of the vitreous carbon is surrounded andencapsulated by the containment portion 15 consisting of a coating 17interior tothe tubular first portion 14 and a coating 18 surrounding theexterior of tubular first portion 14. A loss of integrity of the unit,such as a crack through the vitreous carbon, thereby would expose onlythe particles of the radiation source material exposed on the surface ofthe crack, whereas those particles not on the surface of the crack wouldremain encapsulated in the vitreous carbon body.

Additionalshielding to prevent stray radiation from damaging surroundingtissues can be provided, such as by surrounding the exterior of thevitreous carbon containment body with a dense metal shielding layer 20.While the metal shielding material can be chosen from a wide group ofmetals, lead has been found to be particularly suitable and has beenused in the construction of such devices, as will be described below.

Referring now to FIG. 1 for additional description of the specificembodiment, it can be seen that means, such as connectors 21 and 22associated with each of the two ends of the bore 16, are provided forpassing blood through the device through bore 16 such as withinpyrolytic graphite tube 19. The connectors 21 and 22 extend through themetal shielding layer 20 and communicate with each other through thebore. The connectors are adapted for connection to blood-carryingvessels, such as by Silastic tubing 23 which in turn is joined to bloodvessels in accordance with techniques known in the art. There is noproblem of embrittlement of the Silastic tubing at this point as it issignificantly removed from the radiation source. In operation, bloodflows through the device and is irradiated by irradiation emitted fromirradiation source material 12. Radiation from this material can passthrough the thin inner portion 17 of the vitreous carbon and thepyrolytic graphite tube 16, thereby irradiating blood passing withinbore 16. Irradiation damage to surrounding tissue from stray radiationor radiation emanating outward from radiation source material 12 isprevented by the shielding afforded by the thicker containment portionof vitreous carbon 15 and the metal shielding layer 20.

The use of vitreous carbon as the containment material in this bloodirradiator offers significant advantages. The advantages offered by theuse of a low Z material such as carbon and the presence of the vitreouscarbon as a single integral mass have been mentioned. An additionaladvantage is also offered in that vitreous carbon is a very hard, strongand impermeable material which offers very good containment andexcellent integrity in both normal usage and in case of accident. Inaddition, the radiation source material can be dispersed as a finesuspension within the material which, when fired, will result ininclusion of the source material as an integral part of the vitreouscarbon body. The radiation source material will then be suspended in anidentifiable zone of an otherwise substantially homogeneous vitreouscarbon body.

The irradiation source material will be a radioisotope which may bepresent as a compound and which preferably is a particulate materialsuch as a fine powder. Choice of the particular radioisotope employedwill depend upon the radiation characteristics desired. For irradiationof blood, a beta emitter is generally preferred. In the present device,since elimination of gamma irradiation is desirable in order to limitradiation damage to surrounding tissue, a fairly pure beta emitter isdesired. In the practice of the present invention, thulium-l70 has beenfound to be a particularly desirable radiation source and is preferred.The thuliuml 70 is incorporated into the device as a fine powder of Tm OThe use of thulium-l70 is preferred for several reasons. 'Ihulium-l70 isa fairly pure beta emitter, giving off a 0.96 MeV maximum beta. Inaddition, thulium-l70 has a l25-day physical half-life and is readilyproduced by neutron activation of thuliuml 69. This permits anadditional advantage of constructing the device using thulium-l 69(which is nonradioactive, thus eliminating handling of any radioactivematerial during construction of the device) followed by neutronactivation of a portion of the thulium-l69 to produce the beta-emittingthulium-l 70. In addition, reactivation of the device by neutronactivation after the unit loses effectiveness due to the decay ofthulium-l70 is also possible. Using the neutron activation techniquefollowing manufacture of the device gives importance to the half-life ofthe radioisotope used. Thulium-l70 is also preferred because of theadvantageous l25-day half-life.

Suspension of the radiation source material in the vitreous carbon canbe accomplished by dispersing the radiation source material through aprecursor resin, surrounding this portion of the resin with additionalunloaded resin and carbonizing the entire resin mass so as to produce anintegral vitreous carbon unit. One consideration which must be given tothe choice of the precursor resin used in forming the vitreous carbon isthat it have a high carbon yield. A particular technique for formingvitreous carbon found useful in the construction of the irradiator hasbeen adapted from previously known techniques which are discussed byShigehiko Yamanda in an article A Review of Glasslike Carbons,distributed through the Defense Ceramic Information Center of BattelleMemorial Institute in Columbus, Ohio, Report No. DCIC-68-2, also ReportNo. AD-668 465, April 1968. In accordance with this technique,polyfurfuryl alcohol is cured in the shape desired followed bycarbonization of the polyfurfuryl alcohol to vitreous carbon. Whileother thermosetting resins can be used in the practice of thisinvention, polyfurfuryl alcohol is preferred.

While other prior art techniques can be used in the manufacture ofirradiators in accordance with the present invention and the inventionshould not be limited by disclosed techniques, a blood irradiator inaccordance with the present invention can be manufactured as follows. Asteel mandrel was coated with paraffin and trimmed to the desireddiameter. The radiation source material was mixed with some polyfurfurylalcohol resin, resulting in the grains of the source material beingindividually coated. An active layer of the resin containing the sourcematerial was then painted on the paraffin. A thick containment layer ofpolyfurfuryl alcohol resin was cast about the active layer on themandrel. The containment layer was cast so as to extend at least /a inchbeyond the active layer on each side lengthwise. The polyfurfurylalcohol resin was then cured to rigidity by heating. The heating wassufficient to melt the paraffin which then ran out of the cured resin,permitting easy removal of the steel mandrel. Additional polyfurfurylalcohol resin was dripped down through the tube to coat the inside ofthe active layer. Following coating of the inner surface, the device wasfired so as to carbonize the polyfurfuryl alcohol to vitreous carbon,completely encapsulating the grains of the radiation source material ona microand a macroscale. It is important that the firing to carbonizethe material be done in one step, as there is shrinkage of the resin atthe time that it is fired. If the firing is not done in one step,shrinkage of the material will result in a separation of the layers anda breach of the integrity of thev unit. Firing in one step results inthe formation of an integral mass of vitreous carbon. A metal shieldingmaterial can then be placed around the single-unit vitreous carbon body.Lead in the form of a two-piece can fitting about the vitreous carbonbody in clamshell fashion has been found to be particularly adaptable toconstruction of the device. A small layer of epoxy can be coated aboutthe exterior of the lead shield to insure encapsulation and integrity ofthe unit and provide a smooth outer surface. In the preferredembodiment, a pyrolytic graphite tube runs through the center of thedevice. Alternatively, a vitreous carbon blood interface tube can beformed by dripping the polyfurfuryl alcohol resin down the inside of aquartz tube until the inside is uniformly coated and curing the resin.Following firing in a furnace, which carbonizes the polyfurfuryl alcoholto vitreous carbon, the vitreous carbon tube will shrink about 20percent, permitting easy removal from the quartz tube.

In construction of the device, thulium-169 in the form of Tm O can beused as a radiation source material. This permits construction withoutconcern for radiological hazards or exposure of personnel. In addition,construction of the device is simplified, as the complex techniques ofhandling and working with radioactive materials are eliminated.Following completion of the basic structure, the thulium-l69 can beconverted to radioactive thulium-l70 by neutron activation.

A blood irradiator was constructed in accordance with the specificembodiment of the present invention. A pyrolytic graphite tube having a0.25 mm wall thickness was used as a blood interface because of itsnonthrombogenic character. The inner barrier of vitreous carbonsurrounding the pyrolytic graphite tube was 0.05 mm thick. The innerbarrier was surrounded by a 0.15 mm layer containing Tm O a portion ofwhich was subsequently neutron-activated to thulium-l70. This wassurrounded with a 2.3 mm containment layer of vitreous carbon. The totalweight of the vitreous carbon unit following carbonization was 2 grams.A containment layer of 6.4 mm of lead surrounded the vitreous carbonunit and resulted in a device whose weight was 160 grams. Silastictubing served to connect the graphite tube to arterial and venouscannulas. Following neutron activation, external dose rates were lessthan 50 mR per hour at the surface and a transit dose of 21 rads at aflow rate of 100 ml/min was measured by Fricke dosimetry. The device wasconnected to an arterial-venous shunt (common carotid artery andexternal jugular vein) of a 20 kg goat. Small lymphocytes dropped to 15percent preirradiation level within 7 days and the unit was removed at 11 days. A reciprocal skin allograph performed immediatelypostirradiation survived twice as long (24 days) on the irradiatedanimal as on a nonirradiated control 12 days). Successful reduction ofblood lymphocyte levels was therefore demonstrated.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A tissue irradiator comprising:

a radioisotope material contained in, dispersed through, andencapsulated by a first portion of vitreous carbon, which portion issurrounded and 8 1 encapsulated by a containment portion of vitreouscarbon.

2. A tissue irradiator in accordance with claim 1 for irradiating blood,wherein said containment portion of vitreous carbon is a cylindricalbody having an axial bore therethrough, said radioisotope-containingvitreous carbon portion lies cylindrically about said bore and fullywithin said vitreous carbon containment body, and wherein saidirradiator further comprises means for passing blood through said bore.

3. An in-vivo blood irradiator in accordance with claim 2 furthercomprising:

a metal shielding layer surrounding the exterior of said vitreous carboncontainment body; and wherein said means for passing blood through saidbore comprise connectors associated with each of the two ends of saidbore, said connectors communicating through said bore, said connectorspassing through said surrounding metal layer, and said connectorspermitting connection to blood-carrying vessels.

4. The in-vivo blood irradiator of claim 3 further comprising:

a pyrolytic graphite tube passing through said bore and joining saidconnectors at the two ends of said bore.

5. The in-vivo blood irradiator of claim 4 wherein said radioisotope isthulium-l70.

6. The in-vivo blood irradiator of claim 5 wherein said thulium-l ispresent in the form of Tm O 7. A method of making a tissue irradiatorcomprising:

a. dispersing a radiation source material within a curable resinousmaterial;

b. forming a shaped body of said curable resinous material containingsaid radiation source material and subsequently curing said resinousmaterial;

c. surrounding said shaped body by coating the surfaces of said bodywith additional amounts of said curable resinous material andsubsequently curing said additional resinous material so as to containsaid radiation source material within a shaped structure;

d. firing said resulting shaped structure so as to convert said resinousmaterial to vitreous carbon thereby completely encapsulating saidradiation source material within said vitreous carbon.

8. The method in accordance with claim 7 wherein said resinous materialwhich is carbonized is polyfurfuryl alcohol.

9. The method of claim 8 wherein said radiation source material is Tm Oand which includes thulium- 170.

10. The method in accordance with claim 8 wherein said radiation sourcematerial is Im O and wherein said device is bombarded with neutrons soas to convert a portion of the thulium-l69 to thulium-l70 throughneutron activation.

1. A TISSUE IRRADIATOR COMPRISING: A RADIOISOTOPE MATERIAL CONTAINED IN,DISPERSED THROUGH, AND ENCAPSULATED BY A FIRST PORTION OF VITREOUSCARBON, WHICH PORTION IS SURROUNDED AND ENCAPSULATED BY A CONTAINMENTPORTION OF VITREOUS CARBON.
 2. A tissue irradiator in accordance withclaim 1 for irradiating blood, wherein said containment portion ofvitreous carbon is a cylindrical body having an axial bore therethrough,said radioisotope-containing vitreous carbon portion lies cylindricallyabout said bore and fully within said vitreous carbon containment body,and wherein said irradiator further comprises means for passing bloodthrough said bore.
 3. An in-vivo blood irradiator in accordance withclaim 2 further comprising: a metal shielding layer surrounding theexterior of said vitreous carbon containment body; and wherein saidmeans for passing blood through said bore comprise connectors associatedwith each of the two ends of said bore, said connectors communicatingthrough said bore, said connectors passing through said surroundingmetal layer, and said connectors permitting connection to blood-carryingvessels.
 4. The in-vivo blood irradiator of claim 3 further comprising:a pyrolytic graphite tube passing through said bore and joining saidconnectors at the two ends of said bore.
 5. The in-vivo blood irradiatorof claim 4 wherein said radioisotope is thulium-170.
 6. The in-vivoblood irradiator of claim 5 wherein said thulium-170 is present in theform of Tm2O3.
 7. A method of making a tissue irradiator comprising: a.dispersing a radiation source material withiN a curable resinousmaterial; b. forming a shaped body of said curable resinous materialcontaining said radiation source material and subsequently curing saidresinous material; c. surrounding said shaped body by coating thesurfaces of said body with additional amounts of said curable resinousmaterial and subsequently curing said additional resinous material so asto contain said radiation source material within a shaped structure; d.firing said resulting shaped structure so as to convert said resinousmaterial to vitreous carbon thereby completely encapsulating saidradiation source material within said vitreous carbon.
 8. The method inaccordance with claim 7 wherein said resinous material which iscarbonized is polyfurfuryl alcohol.
 9. The method of claim 8 whereinsaid radiation source material is Tm2O3 and which includes thulium-170.10. The method in accordance with claim 8 wherein said radiation sourcematerial is 169Tm2O3 and wherein said device is bombarded with neutronsso as to convert a portion of the thulium-169 to thulium-170 throughneutron activation.